This invention relates to electronic devices, and more especially integrated circuit devices, including micromechanical switches and to their method of manufacture. Particularly, but not exclusively, the invention relates to integrated circuit photodiode arrays, with addressing of the individual photodiodes being controlled by an associated micromechanical switch.
It has been recognised that micromechanical switches can give lower on-resistance and higher off-resistance than conventional semiconductor switching devices, such as transistors or diodes. Different types of micromechanical switch have been proposed, which use either electrostatic or electromagnetic actuation of a moveable beam to perform the switching operation. Known methods for manufacturing the beam of the switch involve deposition of a beam structure having suitable mechanical and electrical properties over a sacrificial support layer. This sacrificial layer is eventually removed to leave a cavity into which the beam is deflected upon application of the actuation signal. The article xe2x80x9cElectrostatic Polysilicon Microrelays Integrated with MOSFETsxe2x80x9d appearing in Proceedings of the IEEE on Microelectromechanical Systems, 1994, page 97 describes a microrelay comprising a beam supported at both ends with a cavity defined beneath the centre of the beam which is obtained by sacrificial etching of silicon dioxide. This microrelay structure is integrated onto a transistor substrate, so that IC compatibility of the micromechanical device is demonstrated.
A problem with existing methods for manufacturing integrated circuit devices including micromechanical switches is the increased complexity of the manufacturing process resulting from the different components to be integrated onto the device.
According to the present invention, there is provided a method of manufacturing an integrated circuit device, the device comprising a plurality of micromechanical switches and a plurality of thin film circuit components provided on a common substrate, the method comprising:
depositing and patterning a lower electrode pattern which defines bottom contacts for the thin film circuit components and for the micromechanical switches;
depositing and patterning component layers for forming the thin film circuit components over the lower electrode pattern, the component layers defining sacrificial regions over regions of the substrate allocated to the micromechanical switches and defining the thin film circuit components over regions of the substrate allocated to the thin film circuit components;
depositing and patterning a conductive layer to provide an upper electrode pattern, the upper electrode pattern defining top contacts for the thin film circuit components and defining contact beams for the micromechanical switches, the contact beams each extending over a respective sacrificial region;
removing the sacrificial regions of the component layers to define a space between the contact beam and the lower electrode pattern of each micromechanical switch.
In the method of the invention, the lower and upper electrode patterns are shared between the micromechanical switches and the thin film circuit components, thereby reducing the number of additional processing steps required to form the integrated circuit device. Furthermore, layers defining the thin film circuit components also act as the support for the contact beam of the micromechanical switch. In this way, a region of the component layers defines the sacrificial layer of the micromechanical switch, so that the processing steps required for the thin film circuit components and for the switches are shared to the greatest possible extent.
The thin film circuit components may comprise diodes, for example defining a PIN or NIP diode structure, with an upper electrode layer being provided which overlies and directly contacts the diode structure. These diodes may be formed from amorphous silicon layers, and the resulting diode-switch integrated circuit device may define pixels of an image sensor.
The upper electrode layer may be patterned to define a well in the sacrificial region, so that after removal of the sacrificial region, a contact projection is defined on the underside of the contact beam. This contact projection assists in reducing the on-resistance of the switch.
A support layer may be deposited and patterned over the component layers in the regions of the substrate allocated to the micromechanical switches, to provide mechanical support of the contact beam. This may assist in improving the rigidity of the beam and prevent collapse of the beam during subsequent etching processes or during dicing and packaging of integrated circuit components. The removal of the sacrificial regions is preferably carried out using an etchant which leaves the support layer, so that additional support is provided for the contact beam in the finished product.